This invention relates to a scroll-type positive fluid displacement apparatus for compressing, expanding or pumping fluids.
The principles of operation of a scroll apparatus for compressing will be explained with reference to FIG. 1, which shows a stationary involute or spiral-shaped scroll 1 and an orbiting scroll 2 of like shape but displaced and rotated by 180.degree.. The two scrolls 1 and 2 are composed of respective wraps 1a and 2a, each of the same spiral shape but rotated about 180.degree. with respect to each other. The orbiting scroll 2 performs orbital motion about a point without rotation. Thus, a side of the orbiting scroll moves so as to always remain in a parallel position. As shown in the sequence of FIG. 1, compression pockets 5 are formed in the space between the stationary and orbiting scroll members 1 and 2. As the orbiting scroll 2 orbits about a central point 0, the volumes of the pockets 5 are decreased in this compressing operation until they merge into a single, similarly shrinking central outlet pocket 4'. Further compression of the central outlet pocket 4' forces the fluid out a port 4. At the same time, new inlet pockets are formed as shown in FIG. 1(c) at 3, 5, which progressively shrink or are compressed.
In FIG. 2 showing a conventional hermetic type refrigerant compressor using a scroll pump. The orbiting scroll member 2 is supported by a first thrust bearing 21 formed on a support member 8. A pin 2b mounted at the center of the orbiting scroll member 2 is engaged with a drive shaft 6 through an inner bearing 18 such that the orbiting scroll member 2 is being engaged with the stationary scroll member 1. The inner bearing 18 is disposed within a hole formed eccentrically with a generally tubular wall 6a at the top of the drive shaft 6. An outer bearing 19 provides a slideable engagement between the drive shaft 6 and the support member 8. The drive shaft 6 is supported with a first thrust bearing 21 and a second thrust bearing 22 which are formed in the support members 8 and 9. The support member 8 is rigidly attached to an outer cylindrical portion 801 that is positioned around an inner cylindrical space 901. An Oldham coupling 13 is mounted between the orbiting scroll member 2 and the support member 8. The Oldham coupling 13 is a well-known mechanism for inducing orbital motion while preventing rotation. The stationary scroll member 1 is fixed to the supporting members 8 and 9 by fixing means like bolts. A rotor 10 of a motor and an oil cap 7 are fixed to the drive shaft 6, and a stator 11 of the motor is fixed to the supporting member 9, all by means of shrinkage fits, screws or heavy force fits. All parts of the scroll compressor mentioned above are mounted in a shell 12, in an arrangement that the stationary and orbiting scroll members 1 and 2 are positioned above the rotor 10 and the stator 11.
In the construction shown in FIG. 2, when the rotor 10 is rotated, it operates through the Oldham coupling 13 and the drive shaft 6 to cause the orbiting scroll member 2 to move in the orbiting motion such as shown in FIG. 1. When a gaseous fluid is introduced from an inlet tube 16 into the shell 12 during compression operation, the gaseous fluid cools the motor when it passes through a passage 27 formed between the supporting member 9 and the stator 11 and also through a gap formed between the rotor 10 and the stator 11. A gaseous fluid taken up into a compression pocket 5 from an inlet pocket 3 is compressed, and exhausted from an outlet 17 through the outlet port 4. A lubricating oil 15 is fed to the bearings 18 an 20 by centrifugal pumping operation due to the action of the rotating oil cap 7 and an oil hole 23 in the drive shaft 6. Furthermore the lubricating oil which has been fed to the inner bearing 18 is also supplied to the outer bearing 19 and the thrust bearings 21 and 22. The oil used in lubricating is then returned to an oil basin 150 through oil passages 25 and 26. A baffle plate 14 is shaped like a ring, and is fixed in a groove formed on the inside of the supporting member 8 to separate the side of the inlet pocket 3 from the other side of the sliding mechanism in order to prevent the oil, leaking out from the thrust bearing 21, from splashing directly into the inlet pocket 3. A vent hole 24 is formed in the drive shaft 6 so that any gas brought in to the oil cap 7 is exhausted out of the oil cap 7 with the result that the pumping efficiency is kept high during the pumping operation.
The conventional scroll compressor, described above, suffers from the problem that the compressor may be emptied of lubricating oil. This emptying process is caused by foaming produced when liquid refrigerant flows from an evaporator into the oil in the oil basin 150, or when the liquid refrigerant dissolved in the oil during long inactive periods of the scroll compressor is drawn into the scroll compressor upon starting.
As the result of the poor lubrication, the bearings 18, 19, 20, 21 and 22 are likely to be damaged or to seize.